The main objective of this grant is to determine the mechanisms by which carboxypeptidase A1 (CPA1) mutations act as risk factors for chronic pancreatitis in humans. The majority of non-alcoholic cases of chronic pancreatitis develop on the basis of genetic susceptibility, driven by mutations in risk genes that encode digestive enzymes such as cationic trypsinogen (protease serine 1, PRSS1), the pancreatic secretory trypsin inhibitor (serine protease inhibitor Kazal type 1, SPINK1), chymotrypsin C (CTRC) or carboxypeptidase A1 (CPA1). Our studies in previous funding periods clearly defined a pathological pathway associated with increased intra-pancreatic trypsin activity as a result of mutations in PRSS1, SPINK1 and CTRC. Our more recent results on CPA1 mutations, however, indicate that not all genetic risk factors increase trypsin activity. The overarching hypothesis of the current grant is that mutation-induced misfolding and consequent endoplasmic reticulum (ER) stress are the fundamental mechanisms increasing pancreatitis risk in carriers of CPA1 mutations. To test this hypothesis, we will systematically study 28 CPA1 variants and demonstrate that pathogenic CPA1 variants suffer retention and degradation inside the cell with consequently diminished secretion and markedly increased ER stress. In contrast, neutral, non-pathogenic CPA1 variants are secreted normally and do not cause significant ER stress. Furthermore, to obtain insight into the in vivo effects of misfolding CPA1 mutants, we will study a novel knock-in mouse line harboring the human mutation p.N256K in the mouse Cpa1 gene. We expect that pancreatic expression of a misfolding Cpa1 mutant will cause ER stress with increased apoptosis and/or NF?B activation, and may elicit acute and/or chronic pancreatitis. Finally, we will demonstrate that expression of this misfolding Cpa1 mutant in the mouse pancreas sensitizes the pancreas to injury and consequent inflammation and increases pancreatitis responses in experimental models of acute and chronic pancreatitis. Successful completion of these specific aims will firmly establish that mutation-induced misfolding is a relevant disease-mechanism in human chronic pancreatitis and will provide complementary in vitro and in vivo evidence that ER stress and associated signaling pathways mediate increased pancreatitis risk.